Methods and systems for communicating SS7 messages over packet-based network using transport adapter layer interface

ABSTRACT

A transport adapter layer interface (TALI) includes messages, processes, and packet structures for sending and receiving SS7 information over a stream-oriented connection, such as a TCP/IP connection. For example, the TALI interface includes test messages for testing the status of a connection and allow and prohibit messages for enabling and disabling service data communications without invoking a TCP handshaking procedure. The TALI interface also includes SYNC and LENGTH fields for facilitating extraction of individual message packets over a stream-oriented connection.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.09/588,852 filed Jun. 6, 2000 (pending), which is a continuation-in-partof U.S. patent application Ser. No. 09/443,712 filed Nov. 19, 1999,which is a continuation-in-part of U.S. patent application Ser. No.09/205,809 filed Dec. 4, 1998 (now U.S. Pat. No. 6,324,183), and furtherclaims the benefit of U.S. Provisional Application Ser. No. 60/137,988filed Jun. 7, 1999, the disclosures of each of which are incorporatedherein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to methods and systems for communicatingSS7 messages over a packet-based network. More particularly, the presentinvention relates to methods and systems for communicating SS7 messagesover a packet-based network using a transport adapter layer interface.

BACKGROUND ART

The traditional public switched telephone network (PSTN) consists ofsignaling nodes connected via dedicated signaling system 7 (SS7)signaling links. The three primary types of signaling nodes in theconventional PSTN network are service switching points (SSPs), signaltransfer points (STPs), and service control points (SCPs). Serviceswitching points are end office switches that handle both voice and datatraffic. Signal transfer points are switching nodes that route SS7messages between SS7 signaling points. Service control points aredatabases and associated computers that provide data in response to SS7queries. Examples of such data include billing information, 800 numbertranslation information, and number portability information.

These conventional SS7 nodes have typically communicated by sending SS7messages to each other over dedicated SS7 signaling links. While suchsignaling links provide a highly reliable means for communicating SS7traffic, SS7 signaling links provide only fixed bandwidth to a userregardless of the user's needs. As a result, users must install or leasesufficient call signaling bandwidth to handle peak or worst-case trafficconditions. Installing or leasing sufficient call signaling bandwidthfor peak conditions is inefficient since peak conditions rarely occur.Moreover, because SS7 call signaling bandwidth is expensive, thereexists a need for an alternative to dedicated SS7 signaling links.

FIG. 1 is a block diagram of the conventional PSTN network. In FIG. 1,SSPs 100 and 102 communicate with SSPs 104 and 106 through STPs 108,110, 112, and 114. SCP database nodes 116 and 120 provide data inresponse to queries from SSPs 100, 102, 104 and 106 and/or from STPs108, 110, 112, and 114. All of the lines interconnecting the nodes inFIG. 1 represent conventional SS7 signaling links. As stated above, suchlinks are often under-utilized and are expensive to install or lease.

In packet-based networks, such as transmission control protocol/Internetprotocol (TCP/IP) networks, bandwidth can be shared among multipleusers. In addition, the growth and popularity of the global Internethave made components for such networks readily available and costefficient. However, integrating the traditional PSTN network with apacket-based network, such as a TCP/IP network, creates a number ofproblems.

For example, one problem with sending traditional call signaling trafficover a TCP/IP network is that in a TCP/IP network, transmissions betweena sender and a receiver are stream-oriented. That is, TCP software on asending machine is not guaranteed to send data in the same boundariesdefined by a sending application. The amount of data sent over a TCPconnection depends on the window size advertised by the receiver, thenumber of bytes of data that have been acknowledged by the receiver, andthe maximum segment size of the physical network connecting the senderand the receiver. Accordingly, the receiving application may not receivedata in the same boundaries created by the sending application. Thus,when sending call signaling messages over a TCP/IP network, severalmessages may be combined in one TCP segment. Alternatively, a singlecall signaling message may be divided among multiple TCP segments. Inconventional networks, it is the job of the receiving application toparse the incoming data stream and extract the individual packets. Suchparsing is difficult and increases the complexity of applicationprograms that utilize TCP.

Another problem with sending conventional call signaling messages over aTCP/IP connection is that the timeout period for disabling a connectionin TCP is too long for call signaling applications. For example, someimplementations of TCP include a keep-alive timer. The keep-alive timeris reset every time a TCP segment is received. When the timer expires,it causes one side of the connection to determine if the other side isstill operating. No mechanism is specified in the TCP protocolspecifications for determining whether the other side is operating. Inaddition, the timeout period for the keep-alive timer is on the order ofminutes. Thus, one side of a connection could go down and the other sidecould wait for minutes before resetting the connection. Such a longtimeout period wastes resources on the machine that is waiting for datafrom the other side and is unsuitable for telephony applications.

Yet another problem with integrating conventional telephony andpacket-based networks, such as TCP/IP networks, is that TCP/IP requireslengthy handshake procedures for connection establishment andtermination. For example, in order to establish a TCP connection, aclient application sends a synchronization (SYN) packet to a serverapplication. The server application then sends an acknowledgement (ACK)and a SYN back to the client. The client then sends an acknowledgementto the SYN+ ACK from the server. During the initial exchange of SYN andACK messages, the client and server exchange sequence numbers. Once theclient sends acknowledgement to the SYN+ACK to the server, the TCPsoftware on the client machine is in an open state in which data can bereceived from the server and data from the sending application can besent to the server.

In order to terminate a TCP connection, when an application closes aconnection, the TCP software associated with that application sends aFIN packet to the TCP software on the other side of the connection. TheTCP software of the machine that receives the FIN sends an ACK to theFIN and informs the application that a FIN has been received. If theapplication is finished sending data, the application closes theconnection. In response to the application close, the TCP software sendsa FIN to the TCP software that sent the original FIN. In response toreceiving the FIN, the TCP software sends an ACK. Once this ACK is sent,the connection is considered to be closed by both sides of theconnection.

While TCP connection establishment and termination procedures haveproven to be reliable and account for a variety of error conditions,such procedures are cumbersome and require many round trip times inorder to complete. For example, in TCP connection establishment, aminimum of 1.5 round trip times is required. In the TCP connectiontermination scenario described above, at least two round trip times arerequired. In addition, TCP software on both sides of the connection isrequired to maintain state and perform additional processing duringconnection establishment and termination.

For all of these reasons, the number of occurrences of TCP connectionestablishment and termination procedures should be minimized. Forexample, if it is desired to upgrade software in a telephony device thatcurrently communicates with a remote device over a TCP connection, theconnection must be terminated. Connection termination requires thehandshaking procedure discussed above. Once the software is upgraded,the connection must be reestablished. Connection reestablishmentrequires the three-way handshaking procedure described above. Thus,performing a software upgrade requires an initial TCP connectionestablishment, a TCP connection termination, followed by another TCPconnection establishment. These procedures waste resources and should beminimized, especially in high-traffic telecommunications switches.

In light of all these difficulties associated with integratingconventional telephony networks, such as SS7 networks, andstream-oriented packet-based networks, such as TCP networks, thereexists a need for novel methods and systems for integrating thesenetworks that avoid at least some of the difficulties associated withthe prior art.

DISCLOSURE OF THE INVENTION

The present invention includes methods and systems for communicating SS7messages between signaling nodes over a packet-based network using atransport adapter layer interface. As used herein, the phrase transportadapter layer interface refers to an interface that resides above thetransport layer in the TCP protocol stack that facilitates integrationbetween the SS7 protocol stack and the TCP/IP protocol stack. Such aninterface includes functionality for prohibiting and allowingcommunications over a socket without invoking conventional TCPconnection establishment and termination handshaking procedures. Inaddition, the interface provides monitor and test messages that arerespectively used to measure performance and test the status of aconnection. The interface also provides a mechanism for encapsulatingSS7 messages that allows individual message identification over astream-oriented connection.

Embodiments of the invention will be described below as modules, layers,or processes for implementing SS7 and IP communications functions. It isunderstood that these modules, layers, or processes can be implementedas hardware, software, or a combination of hardware and software. Forexample, transport adapter layer interface functionality is describedbelow as a process implemented on a data communications module. The datacommunications module may include hardware, such as a microprocessor andassociated memory, for executing and storing programs. The TALI processmay be executed by the microprocessor to perform the TALI functionsdescribed below.

Accordingly, it is an object of the invention to provide novel methodsand systems for communicating SS7 messages over a stream-orientedpacket-based network that avoids the problems with conventionalstream-oriented packet-based networks.

It is another object of the invention to provide methods and systems forallowing and prohibiting service data communications over astream-oriented connection without invoking a TCP handshaking procedure.

It is yet another object of the invention to provide methods and systemsfor identifying message packets received over a stream-orientedconnection.

Some of the objects of the invention having been stated hereinabove,other objects will be evident as the description proceeds, when taken inconnection with the accompanying drawings as best described hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described withreference to the accompanying drawings of which:

FIG. 1 is a block diagram illustrating the conventional PSTN network;

FIG. 2 is a block diagram of an exemplary operating environment forembodiments of the present invention;

FIG. 3 is a block diagram of a signaling gateway capable of sending SS7messages over a packet-based network using a transport adapter layerinterface according to an embodiment of the present invention;

FIGS. 4(a) and 4(b) are block diagrams illustrating the relationshipsbetween the SS7 and IP protocol stacks and methods for integrating theprotocol stacks using a transport adapter layer interface according toembodiments of the present invention;

FIG. 5 is a block diagram illustrating an exemplary packet structure forencapsulating of SCCP messages using a transport adapter layer interfaceaccording to an embodiment of the present invention;

FIG. 6 is a flowchart illustrating exemplary steps that may be performedby a signaling gateway in encapsulating SCCP messages using a transportadapter layer interface according to an embodiment of the presentinvention;

FIG. 7 is a block diagram illustrating an exemplary packet structure forencapsulating MTP3 messages using a transport adapter layer interfaceaccording to an embodiment of the present invention;

FIG. 8 is a block diagram illustrating an exemplary packet structure forencapsulating SS7 messages using an ATM adaption layer and a transportadapter layer interface according to an embodiment of the presentinvention;

FIG. 9 is a flowchart illustrating exemplary steps for identifyingindividual message packets received over a stream-oriented connectionaccording to an embodiment of the present invention;

FIG. 10 is a flowchart illustrating exemplary steps for monitoringconnection status using transport adapter layer interface messagesaccording to an embodiment of the present invention;

FIG. 11 is a flowchart illustrating exemplary steps for allowing andprohibiting communications using a transport adapter layer interfaceaccording to embodiments of the present invention; and

FIG. 12 is a flowchart illustrating exemplary steps for measuring roundtrip time using transport adapter layer interface messages according toan embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 illustrates an exemplary operating environment for embodiments ofthe present invention. In FIG. 2, conventional SS7 network elements,such as SSPs 200, 202, and 204 and SCP 206, communicate with each otherover SS7 network 208. IP nodes, such as media gateways (MGs) 210, 212,and 214, media gateway controllers (MGCs) 216 and 218 and Internetservice provider (ISP) 220, communicate with each other over firstpacket-based network 222. Similarly, signaling gateways 224 and 226communicate with MGCs 216 and 218 and with SCP 228 via secondpacket-based network 230. First and second packet-based networks 222 and230 may each comprise IP networks. Moreover, first and secondpacket-based networks 222 and 230 may be the same logical network. Thereason that networks 222 and 230 are illustrated separately in FIG. 2 isthat first packet-based network 222 carries packetized media streamcommunications between MGs, and media control information between MGCsand MGs, and second packet-based network 230 carries call signalingtraffic to and from SGs 224 and 226.

The conventional SS7 network elements, such as SSPs and SCPs, aredescribed in detail above. Hence a description thereof will not berepeated herein. The additional network elements illustrated in FIG. 2include media gateways 210, 212, and 214, media gateway controllers 216and 218, signaling gateways 224, and 226, and Internet service provider(ISP) 220. Media gateways 210, 212, and 214 encapsulate media streamcommunications, such as audio, video, and data, in IP packets to betransmitted over first packet-based network 222. An example of aprotocol used to send media stream communications over a packet-basednetwork is the real time protocol (RTP) as defined in RFC 1889, RTP: ATransport Protocol for Real Time Applications, Jacobson et al., January1996.

MGCs 216 and 218 control MGs 210, 212, and 214 using a control protocol.An example of a control protocol that may be implemented by MGCs 216 and218 is the media gateway control protocol as described in Media GatewayControl Protocol (MGCP),http://search.ietf.org/internet-drafts/draft-huitema-mejaco-mgcp-v0r1-05.txt,Feb. 21, 1999. ISP 220 provides Internet services to subscribers.Accordingly, ISP 220 may include a network access server to provide useraccess to the Internet.

Signaling gateways 224 and 226 implement an interface between SS7network 208 and second packet-based network 230. In a preferredembodiment of the invention, signaling gateways 224 and 226 provide atransport adapter layer interface to allow conventional networkelements, such as SSPs 200, 202, and 204, to communicate with IP networkelements, such as MGCs 216 and 218. However, the transport adapter layerinterface is not limited to communications between SSPs and MGCs. Forexample, the transport adapter layer interface according to embodimentsof the present invention may also be used to communicate call signalingmessages to IP-based SCPs, such as SCP 228 and other devices equippedwith an IP interface.

FIG. 3 is a block diagram illustrating a signaling gateway forimplementing transport adapter layer interface functionality accordingto an embodiment of the present invention. In FIG. 3, signaling gateway224 includes SS7 link interface module (LIM) 300 for sending andreceiving SS7 messages over an SS7 network and data communicationsmodule (DCM) 302 for sending and receiving SS7 messages over one or morestream-oriented connections. Signaling gateway 224 may also includeadditional modules, such as database service module (DSM) 304, forproviding SCCP and database services. Modules 300, 302 and 304 areconnected by an interprocessor message transport (IMT) bus 306. IMT bus306 is preferably a dual ring counter rotating bus for increasedreliability.

Link interface module 300 includes a number of processes for sending andreceiving SS7 messages over SS7 links. In the illustrated embodiment,link interface module 300 includes MTP level 1 and 2 process 307 forperforming SS7 layer 1 and 2 processing of incoming messages. I/O queue308 enqueues incoming and outgoing SS7 messages. Message discriminationprocess 309 determines whether incoming messages are addressed tosignaling gateway 224 or to another node. For example, messagediscrimination process 309 may analyze the SS7 destination point code inan incoming message to determine whether the message is addressed tosignaling gateway 224 or to another node. If message discriminationprocess 309 determines that the message is addressed to signalinggateway 224, message discrimination process 309 forwards the message tomessage distribution process 310. Message distribution process 310routes the message to another internal module for further processing.

DSM 304 provides database and SCCP service for SS7 messages.Accordingly, DSM 304 may include signaling connection routing control(SCRC) and SCCP processes 312 and 314 for interpreting SCCP layerinformation of incoming messages and routing the messages to databaseprocess 316. Database process 316 may perform a lookup in database 318to obtain routing or other information for an incoming message. Forexample, database 318 may be a number portability database, a circuitidentification code routing database, a billing code database, or otherdatabase for performing routing or other functionality. Routing process320 routes the message to the appropriate module for outgoing processingbased on MTP layer 3 information in the message.

DCM 302 includes transport adapter layer interface process 322 forperforming transport adapter layer interface functionality. Suchfunctionality includes encapsulating SS7 messages in a transport adapterlayer interface packet to be sent over a stream-oriented connection,allowing and prohibiting communication over a stream-orientedconnection, monitoring the other end of the stream-oriented connection,etc. DCM 302 preferably also includes a stream-oriented communicationprocess such as TCP/IP process 324. TCP/IP process 324 performsconventional TCP/IP protocol stack functions. Such functions includereliable delivery of TCP/IP packets, flow control, packet sequencing,and other stream-oriented transport functionality.

FIG. 4(a) is a block diagram illustrating the relationships between theSS7 protocol stack and the transport adapter layer interface protocolstack according to an embodiment of the present invention. In FIG. 4,SS7 protocol stack 400 includes MTP layer 1 402, MTP layer 2 404, andMTP layer 3 406. MTP layer 1 402, also referred to as the physicallayer, communicates with hardware to send and receive data over aphysical medium. MTP layer 2 404, referred to as the data link layer,provides error correction/detection and properly sequenced delivery ofSS7 message packets. MTP layer 3 406, also referred to as the networklayer, is responsible for SS7 message routing, message discrimination,and message distribution.

Residing above MTPs layers 1-3 is the user parts and application partslayer 408. User parts and application parts layer 408 is divided intoISDN user part (ISUP) layer 410, signaling connection control part(SCCP) layer 412 and transaction capabilities application part (TCAP)layer 414. ISDN user part layer 410 performs SS7 call setup and calltear-down functions. SCCP layer 412 performs signaling connectioncontrol part functions, such as database subsystem addressing. TCAPlayer 414 is used for database transactions, such as 800 numbertranslations, number portability transactions, and billing transactions.Finally, SS7 application layer 416 can perform any function that usesthe underlying services provided by SS7. Examples of such applicationsinclude billing applications, network monitoring applications, etc.

TALI protocol stack 418 includes IP protocol stack portion 420, TALIportion 422, and SS7 portion 424. IP protocol stack portion 420 includesa physical and MAC layer 426, a network layer 428, and a transport layer430. Physical and MAC layer 426 interfaces with network hardware forcommunication between connected machines and transports network framesbetween machines connected to the same network. Network layer 428handles routing and addressing of datagrams between different physicalnetworks. In a preferred embodiment of the invention, network layer 428performs addressing and routing functions according to the Internetprotocol, such as Internet protocol version 4 or Internet protocolversion 6. Transport layer 430 provides communication betweenapplication programs. In a preferred embodiment of the presentinvention, transport layer 430 includes stream-oriented transportsoftware, such as TCP software, for implementing reliablestream-oriented transport between applications.

It should be noted that although TALI protocol stack 418 illustrated inFIG. 4(a) includes MTP3 layer 406, MTP layer 3 functionality, other thanprocessing point codes, is optional and may be omitted from TALIprotocol stack 418.

According to an important aspect of the present invention, transportadapter layer interface portion 422 includes functions and packetstructures that facilitate interoperability between the SS7 and TCPprotocols. For example, transport adapter layer interface portion 422includes packet structures that facilitate extraction of SS7 packetsfrom a TCP data stream, commands for allowing and prohibitingconnections without invoking TCP connection establishment andtermination procedures, monitor messages for measuring round trip time,and test messages for determining whether a TCP connection is enabled ordisabled. Each of these functions will be discussed in more detailbelow.

Traditional SS7 devices 436, such as SSPs, STPs, and SCPs, communicatewith signaling gateway 224 using SS7 protocol stack 400. TCP/IP devices438, such as MGCs and IP-based SCPs, communicate with signaling gateway224 using TALI protocol stack 418. Accordingly, signaling gateway 224preferably includes software for implementing both SS7 protocol stack400 and TALI protocol stack 418.

As illustrated in FIG. 3, SS7 protocol stack 400 may be implemented byor on LIM 300 and TALI protocol stack 418 may be implemented by or onDCM 302. However, the present invention is not limited to such animplementation. For example, in an alternative embodiment of theinvention, SS7 protocol stack 400 and TALI protocol stack 418 may beimplemented on a single card or module within signaling gateway 224 orin another node in which SS7 and IP communication capability isdesirable.

FIG. 4(b) is a block diagram illustrating an alternative implementationof the TALI protocol stack according to an embodiment of the presentinvention. In FIG. 4(b), SS7 protocol stack 400 a includes MTP3, SCCP,TCAP, ISUP, and application layers 406, 412, 414, and 416 that areidentical to the correspondingly numbered layers described with respectto FIG. 4(a). However, in FIG. 4(b) MTP layers 1 and 2 are replaced byasynchronous transport mode (ATM) layer 450, ATM adaption layer 5 452,and signaling ATM adaption layer 454. Layers 450, 452, and 454 performfunctions for transmitting SS7 traffic over a broadband network, such asan ATM network.

TALI protocol stack 418 a includes MAC, network, transport, TALI, andSS7 layers 426, 428, 430, 422, and 424, that are identical to thecorrespondingly numbered layers described with respect to FIG. 4(a).However, TALI protocol stack 418 a includes signaling ATM adaption layer(SAAL) 454 to provide sequencing of SS7 data transferred across a TCP/IPconnection. When TALI protocol stack 418 a is implemented without SAALlayer 454, as illustrated in FIG. 4(a), the SS7 sequence number, whichis included in the SS7 MTP2 header, is not transferred across a TCP/IPconnection. This sequence number is used to preserve message sequencingand to support complex SS7 procedures involving MSU retrieval duringlink changeover and changeback. Changeover is an SS7 procedure whereby alink request is sent over one SS7 link to move SS7 traffic from thatlink to another SS7 link. Changeback is an SS7 procedure for moving theSS7 traffic back to the original link. TALI protocol stack 418illustrated in FIG. 4(a) without SAAL layer 454 still guarantees correctsequencing of SS7 data because TCP layer 430 provides sequencing of TCPsegments that carry the SS7 traffic.

When TALI protocol stack 418 a is implemented with SAAL layer 454, thesequence number of the SS7 MSU is part of the data transferred across aTCP/IP connection. This sequence number may be included as a header, atrailer, or in any other portion of a transport adapter layer interfacepacket. In the illustrated example, the sequence number is a 24-bitvalue included in a service specific connection oriented protocol(SSCOP) trailer provided by SAAL layer 454. This 24-bit sequence numberserves the same purpose as the 8-bit SS7 sequence number. Accordingly,TALI protocol stack 418 a illustrated in FIG. 4(b) can be used for SS7changeover and changeback with data retrieval and can minimize MSU losswhen SS7 links are deactivated.

SCCP Encapsulation Using TALI

FIG. 5 illustrates a packet structure for encapsulating SCCP MSUs in IPpackets using the transport adapter layer interface according to anembodiment of the present invention. In FIG. 5, SS7 MSU 500 includesSCCP layer information 502 and TCAP layer information 504 that areencapsulated in service portion 506 of TALI packet 508. SS7 MSU 500 alsoincludes service indicator octet 510 and routing label 512. In oneembodiment of the invention, service indicator octet 510 and routinglabel 512 may be encapsulated directly in service portion 506 of TALIpacket 508. However, in the illustrated embodiment, service indicatoroctet 510 and routing label 512 are omitted from TALI packet 508.Omitting the service indicator octet and routing label information fromthe TALI packet simplifies processing by the receiving TALI process.

Rather than encapsulating service indicator octet 510 and routing label512 directly in service field 506 of TALI packet 508, TALI protocolsoftware according to embodiments of the present invention may storeinformation from SIO 510 and routing label 512 in other informationfields. For example, the destination point code from routing label 512may be stored in the SCCP called party point code field of SCCP layer502. Similarly, the originating point code from routing label 512 may bestored in the SCCP calling party point code field of routing label 512.Message type identification information from SIO 510 may be merged toOPCODE field 514 of TALI packet 508. For example, OPCODE field 514 maystore information for identifying the message type. In the illustratedembodiment, OPCODE field 514 may be set to a predetermined value foridentifying the message as an SCCP message. The remaining fields of SS7MSU 500 are preferably omitted from TALI packet 508. That is, SS7 layer2 information, opening flags, closing flags, and frame check sequencesare preferably omitted from TALI packet 508. This information can beomitted because the TCP/IP protocol stack provides analogous functionsto SS7 layers 1 and 2. Omitting SS7 layers 1 and 2 from TALI packet 508decreases overhead for sending packets over a network.

In addition to service field 506 and OPCODE field 514, TALI packet 508also includes LENGTH field 516 and SYNC field 518. LENGTH field 516specifies the length of the service portion of the data packet. SYNCfield 518 contains a predetermined bit sequence for identifying thestart of TALI packet 508. LENGTH field 516 and SYNC field 518 may beused by receiving TALI protocol software to extract individual TALIpackets from a stream-oriented connection. Thus, the TALI packetstructure in FIG. 5 solves the problem of receiving data over astream-oriented communication and delivers individual TALI packets to anapplication. This simplifies application design, as will be discussed inmore detail below.

TALI packet 508 is encapsulated in data portion 520 of network frame522. Network frame 522 may be any suitable frame for delivering packetsto machines connected to the same network. For example, network frame522 may be an Ethernet frame. Accordingly, network frame 522 includes amediated access control (MAC) header 524. IP header 526 follows MACheader 524. Finally, TCP header 528 follows IP header 526. The structureof headers 524, 526, and 528 is known to those of ordinary skill in theart and need not be described herein.

FIG. 6 is a flowchart illustrating exemplary steps that may be performedby TALI process 322 illustrated in FIG. 3 for performing TALIencapsulation of an SCCP MSU. In FIG. 6, in step ST1, TALI process 322receives an SS7 MSU. The SS7 MSU may originate from an SS7 node, such asan SSP. In step ST2, TALI process 322 discards MTP layer 2 information,SRC, and flags from the SCCP MSU. In step ST3, TALI process 322 placesthe destination point code from the routing layer into the called partyaddress field of the SCCP layer. In step ST4, TALI process 322 placesthe originating point code from the routing label in the calling partyaddress field of the SCCP layer. It is understood that steps ST3 and ST4are optional and can be omitted if the entire MTP3 portion of the SCCPMSU is encapsulated in the service portion of the TALI packet.

In step ST5, TALI process 322 sets the SYNC field in the header of theTALI packet to indicate the beginning of the TALI packet. In ST6, TALIprocess 322 sets the OPCODE field of the TALI packet to SCCP. In stepST7, TALI process 322 sets the LENGTH field is set to the number ofoctets in the service field of the TALI packet. Finally, in step ST8,TALI process 322 sends the packet to TCP/IP process 324 for TCP/IPencapsulation and transmission to an external node.

The steps for processing an incoming TALI packet are essentially thereverse of the steps illustrated in FIG. 6. Novel steps for processingincoming TALI packets will be discussed in more detail below in thesection entitled “Identifying Individual Message Packets Received OverStream-Oriented Connection.”

MTP3 Encapsulation Using TALI

FIG. 7 is a block diagram illustrating an exemplary packet structure forencapsulating MTP3 messages in IP packets according to a preferredembodiment of the present invention. As used herein, an MTP3 message isan SS7 message that is not an SCCP or an ISUP message. These messagescorrespond to service indicator values of 0-2, 4, and 6-15. In FIG. 7,SS7 MSU 700 includes layer 2 702, layer 3 703, and opening and closinginformation 704 and 706. Unlike the example illustrated in FIG. 5, inthis example, all of layer 3 information is encapsulated in serviceportion 506 of TALI packet 508. Like the example illustrated in FIG. 5,layer 2 information 702, and opening and closing information 704 and 706are preferably discarded.

In TALI packet 508, LENGTH field 516 is set to the length of serviceportion 506. OPCODE field 514 is set to a predetermined value foridentifying an MTP3 packet. SYNC field 518 is set to a predeterminedvalue for identifying the start of TALI packet 508. TALI packet 508 isencapsulated in network frame 522 in the same manner described abovewith respect to FIG. 5. Thus, the present invention provides a methodfor encapsulating MTP3 messages other than ISUP and SCCP messages innetwork frames using a transport adapter layer interface.

SAAL Encapsulation Using TALI

As illustrated above with regard to FIG. 4(b), one embodiment of thetransport adapter layer interface protocol stack includes a SAAL layer.TALI also provides a corresponding SAAL OPCODE that indicates that aSAAL message is being transported. This OPCODE may be used to transportany type of SS7 message, including ISUP messages, SCCP messages, andMTP3 messages that includes SAAL information. In addition, the SAALOPCODE may be used to transport non-SS7 messages, such as SMLpeer-to-peer messages.

FIG. 8 illustrates encapsulation of SAAL messages using a transportadapter layer interface according to an embodiment of the presentinvention. In FIG. 8, SS7 MSU 800 includes layer 2 and layer 3 portions802 and 803 and opening and closing portions 804 and 805, as previouslydescribed. Layer 3 portion 802 includes an SIO value 806, a routinglabel 807, and other layer 3 information 808. Other layer 3 information808 can include ISUP information, application part information, or MTP3information, as previously described. In the illustrated embodiment, allof layer 3 information 803 is encapsulated in service portion 810 ofTALI packet 812.

TALI packet 812 includes LENGTH field 814, OPCODE field 816, and SYNCfield 818. In addition, TALI packet 812 includes SSCOP trailer 820.LENGTH field 814 specifies the number of octets in service portion 810,OPCODE field 816 is set to a predetermined value for identifying TALIpacket 812 as a SAAL packet, and SYNC field 818 is set to apredetermined value for indicating the beginning of TALI packet 812.SSCOP trailer 820 contains a sequence number for sequencing TALI servicedata packets when a TCP/IP link fails. TALI packet 812 is encapsulatedin network frame 522 in the manner described above. SAAL decapsulationcan occur in a manner similar to that described above with respect toFIG. 6 if service portion 810 of TALI packet 812 contains an SS7 MSU. Ifservice portion 810 of TALI packet 812 contains a SAAL peer-to-peermessage, decapsulation may be performed by the SAAL layer, rather thanthe TALI layer.

TALI State Machine

Table 1 shown below is a state machine for the TALI protocol. In Table,1, columns represent protocol states and the rows represent events thatmay or may not cause transitions between protocol states. Blank cells inthe table indicate that no action occurs for a given state in responseto a given event. Cells with text indicate functions performed by TALIprotocol implementations and state transitions that occur in response toevents.

The states in the TALI protocol are: out-of-service (OOS), connecting,near end prohibited—far end prohibited (NEP-FEP), near endprohibited—far end allowed (NEP-FEA), near end allowed—far endprohibited (NEA-FEP), and near end allowed—far end allowed (NEA-FEA). Inthe out of service state, a TCP connection has either not beenestablished or has been disabled. In the connecting state, a TCPconnection is being established between TCP software associated withTALI endpoints. “Prohibited” refers to a condition in which a TCPconnection is established but TALI service messages are not permitted tobe sent to the side for which message flow is prohibited. Finally,“allowed” refers to the willingness of one side of a connection toaccept TALI service messages. As used herein, TALI service messages aremessages that carry application data. TALI messages are messages such asallow, prohibit, monitor, and test, that carry TALI control information.SAAL messages that are not used to carry application data also fall intothe TALI messages group. Thus, when in the prohibited state, TALImessages are permitted, while TALI service messages are not permitted.

The events listed in column 1 of Table 1 include timer expirations,receipt of messages, protocol violations, etc. The TALI protocolincludes four main timers: T1, T2, T3, and T4. The T1 timer representsthe time interval between the origination of a test message at each TALIimplementation. Each time T1 expires, a TALI implementation should senda test message. The test message will be discussed in more detail belowwith regard to monitoring the status of a TALI connection.

The timer T2 represents the amount of time that a TALI implementationhas to return an allow or a prohibit message in response to a testmessage. If the far end of a TALI connection fails to reply with anallow or prohibit message before T2 expires, the sender of the testmessage treats the T2 message as a protocol violation (PV).

The timer T3 controls the length of time that the near end of the TALIconnection should process service data that is received from the far endof a TALI connection after a management prohibit traffic event hasoccurred at the near end. As used herein, a “management event” is anaction performed by an application that resides above and uses the TALIlayer. The timer T3 is used when a transition from NEA-FEA (both endsallowed to send service data) to NEP-FEA (only far end willing to sendservice data) occurs. When an endpoint transitions to the prohibitedstate, the endpoint is indicating that the endpoint desires to stopreceiving service message traffic. That is, if A and B are theendpoints, and endpoint B wishes to not receive service message traffic,then endpoint B sends a prohibit message to endpoint A. After sendingthe prohibit message, endpoint B receives and processes traffic for T3seconds. After T3 expires, no service messages are processed by endpointB. Endpoint A starts diverting traffic to a node other than endpoint Bonce it receives the prohibit message from endpoint B.

Some data may have been given to the TCP layer at endpoint A fortransmission after endpoint B sent the prohibit message but before theprohibit message was received by endpoint A. The application at endpointA does not have control over messages already given to TCP. If endpointB did not wait some amount of time, then endpoint B would discard validmessages. Endpoint A would stop passing data to the TCP layer once ithas received the prohibit message.

The T4 timer represents the time interval between the origination of themonitor message. Each time T4 expires, the TALI implementation shouldsend a monitor message. The use of monitor messages to measure the roundtrip time of a connection will be discussed in more detail below.

Other messages illustrated in the events column of Table 1 are special(spcl) messages and extended service (xsrv) messages. Extended servicemessages are use to transport types of service traffic other than thosedescribed above. Special messages are vendor specific messages used toprovide services other than those provided by TALI.

Another feature of the invention illustrated in Table 1 is the use ofmonitor messages to identify the TALI software version of the far end ofa TALI connection. For example, according to Table 1, when animplementation receives a monitor message in any state except out ofservice or connecting, the implementation updates the TALI version ofthe far end of the connection. Exemplary fields in the monitor messageused to identify TALI version will be discussed in more detail below.

The following description illustrates an exemplary path through thestate machine illustrated in Table 1. First, TCP software associatedwith a near end TALI implementation may establish a TCP connection withTCP software associated with a far end TALI implementation. During theTCP connection establishment phase, both TALI implementations are in theconnecting state. Once a TCP connection is established, both TALIimplementations are in the NEP-FEP state, indicating that TALI servicemessages cannot be sent. When the near end TALI implementation receivesan allow message, the state machine switches to the NEP-FEA state. Inthe NEP-FEA state, the near end TALI implementation will send an allowmessage when a management allow traffic event occurs. As used herein,the phrase “management allow traffic event” refers to an event thatnotifies the TALI implementation that service messages can be sent onthe socket in question. Once the near end TALI implementation sends anallow message, the state machine transitions to the NEA-FEA state. Inthe NEA-FEA state, both TALI implementations can send and receive TALIservice messages. TABLE 1 TALI State Machine STATE→ EVENT ↓ OOSConnecting NEP-FEP NEP-FEA NEA-FEP NEA-FEA T1 Timer Send test Send testSend test Send test Expired Start T1 Start T1 Start T1 Start T1 Start T2Start T2 Start T2 Start T2 T2 Timer PV PV PV PV Expired T3 Timer PV PVExpired T4 Timer Send moni Send moni Send moni Send moni Expired StartT4 Start T4 Start T4 Start T4 Received Send proh Send proh Send alloSend allo Test Message Received Stop T2 Stop T2 Stop T2 Stop T2. AllowNEP-FEA NEA-FEA Message Received Stop T2. Stop T2 Stop T2 Stop T2.Prohibit Send proa Send proa Send proa Flush or re- Message NEP-FEProute data Send proa NEA-FEP Received Stop T3 Stop T3 ProhibitAcknowledg- ment Message Received Update ‘far end Update ‘far end Update‘far end Update ‘far end Monitor version’ based version’ based version’based version’ based Message on moni content on moni content on moni onmoni Convert moni to Convert moni to content content mona mona Convertmoni to Convert moni to send mona send mona mona mona send mona sendmona Received Implementation Implementation ImplementationImplementation Monitor dependent dependent dependent dependentAcknowledg- processing. processing. processing. processing. ment MessageReceived PV If T3 running PV Process data Service Process data MessageElse PV Received If ‘far end If ‘far end If ‘far end If ‘far end ‘mgmt’version’ <2.0 version’ <2.0 version’ <2.0 version’ <2.0 Message PV PV PVPV Else Else Else Else Process Process Process Process according to theaccording to the according to according to nodes 2.0 mgmt nodes 2.0 mgmtthe nodes 2.0 the nodes 2.0 capabilities. capabilities. mgmt mgmtcapabilities. capabilities. Received If ‘far end If ‘far end If ‘far endIf ‘far end ‘xsrv’ version’ <2.0 version’ <2.0 version’ <2.0 version’<2.0 Message PV PV PV PV Else Else Else Else Process Process ProcessProcess according to the according to the according to according tonodes 2.0 xsrv nodes 2.0 xsrv the nodes 2.0 the nodes 2.0 capabilities.capabilities. xsrv xsrv capabilities. capabilities. Received If ‘far endIf ‘far end If ‘far end If ‘far end ‘spcl’ version’ <2.0 version’ <2.0version’ <2.0 version’ <2.0 Message PV PV PV PV Else Else Else ElseProcess Process Process Process according to the according to theaccording to according to nodes 2.0 spcl nodes 2.0 spcl the nodes 2.0the nodes 2.0 capabilities. capabilities. spcl spcl capabilities.capabilities. Connection start T1 Established start T2 start T4 ifsock_allowed == TRUE Send moni Send allo Send test NEA_FEP Else Sendmoni Send proh Send test NEP_FEP Connection PV PV PV PV Lost ProtocolStop all timers Stop all timers Stop all timers Stop all timersViolation Close the socket Close the socket Close the Close theConnecting Connecting socket socket Connecting Connecting Manage- Openment Open the Socket socket Connect- ing Manage- Close the Stop alltimers Stop all timers Stop all timers Stop all timers ment Close socketClose the socket Close the socket Close the Close the Socket OOS OOS OOSsocket socket OOS OOS Manage- sock_all sock_allowed = sock_allowed =sock_allowed = sock_allowed = sock_allowed = ment Prohibit owed = FALSEFALSE FALSE FALSE FALSE Socket FALSE Send proh Send proh Start T3 StartT3 NEP-FEP NEP-FEA Manage- sock_all sock_allowed = sock_allowed =sock_allowed = sock_allowed = sock_allowed = ment Allow owed = TRUE TRUETRUE TRUE TRUE Traffic TRUE Send allo. Send allo. NEA-FEP NEA-FEA UserPart Reject Reject data Reject data Reject data Reject data Send dataMessages data Request If ‘far end If ‘far end If ‘far end If ‘far endfrom higher version’ <2.0 version’ <2.0 version’ <2.0 version’ <2.0software Ignore/reject Ignore/reject Ignore/reject Ignore/reject layersto Else Else else Else send ‘mgmt’ Process Process Process Processmessages according to the according to the according to according tonodes 2.0 mgmt nodes 2.0 mgmt the nodes 2.0 the nodes 2.0 capabilities.capabilities. mgmt mgmt capabilities. capabilities. Request If ‘far endIf ‘far end If ‘far end If ‘far end from higher version’ <2.0 version’<2.0 version’ <2.0 version’ <2.0 software Ignore/reject Ignore/rejectIgnore/reject Ignore/reject layers to Else Else Else Else send ‘xsrv’Process Process Process Process messages according to the according tothe according to according to nodes 2.0 xsrv nodes 2.0 xsrv the nodes2.0 the nodes 2.0 capabilities. capabilities. xsrv xsrv capabilities.capabilities. Request If ‘far end If ‘far end If ‘far end If ‘far endfrom higher version’ <2.0 version’ <2.0 version’ <2.0 version’ <2.0software Ignore/reject Ignore/reject Ignore/reject Ignore/reject layersto Else Else Else Else send ‘spcl’ Process Process Process Processaccording to the according to the according to according to nodes 2.0spcl nodes 2.0 spcl the nodes 2.0 the nodes 2.0 capabilities.capabilities. spcl spcl capabilities. capabilities.

Identifying Individual Message Packets Received over Stream-OrientedConnection

As discussed above, one of the problems associated with receiving dataover a stream-oriented connection, such as a TCP connection, is that thepacket boundaries created by a sending application may not be preservedby the underlying TCP software. As a result, the receiving applicationmay not receive data in the intended units. The present embodimentsolves this problem with regard to TALI packets using the SYNC andLENGTH fields. FIG. 9 is a flowchart illustrating exemplary steps thatmay be performed by TALI process 322 illustrated in FIG. 3 foridentifying TALI packets received over a stream-oriented connection. Instep ST1, a stream-oriented connection such as a TCP connection isestablished between endpoints. The endpoints may be a signaling gatewayand a media gateway controller. In step ST2, TALI process 322 receivesdata over the connection. In step ST3, TALI process 322 reads apredetermined number of bytes to extract the header from the stream ofdata received over the connection. The predetermined number of bytes isequal to the size of the header as set by the TALI version. For example,the header may be twenty bytes in length.

In step ST4, TALI process 322 breaks the header into SYNC, OPCODE, andLENGTH fields. In step ST5, TALI process 322 determines whether thevalue in the SYNC field is valid. If the value in the SYNC field is notvalid, TALI process 322 treats the message as a protocol violation. IfTALI process 322 determines that the SYNC field is valid, TALI process322 may then determine whether the LENGTH and OPCODE fields are valid(step ST7). In step ST8, TALI process 322 reads the next LENGTH bytes inthe data stream after the header. In step ST9, TALI process 322 passesthe packet up the protocol stack to be processed by the TALI statemachine. Once the TALI packet has been passed up the protocol stack,TALI process 322 returns to step ST3 to read the next data header.Because TALI process 322 uses the SYNC and LENGTH fields to determinepacket boundaries, SS7 application design is greatly simplified. Thereis no need for an SS7 application to be concerned with packetboundaries.

TALI Peer-To-Peer Messages

TALI peer-to-peer messages are messages that are transmitted by the TALIlayer of one side of a stream-oriented connection and that areterminated by the TALI layer of the other side of a stream-orientedconnection. The TALI peer-to-peer messages that are described hereininclude test messages for testing the status of a connection, allow andprohibit messages for allowing and prohibiting communications over aconnection without invoking TCP connection establishment or terminationprocedures, and monitor messages for measuring the round trip time of aconnection. Each of these messages will now be discussed in more detail.

Test messages are used by a TALI implementation to query the remote endof a TALI connection with respect to the willingness of the remote endto carry SS7 service data. Test messages are preferably sentperiodically by each TALI implementation based on a predeterminedtimeout value. Upon receiving a test message, a TALI implementation mustreply with either a prohibit or an allow message to indicate whether theTALI implementation will carry SS7 service data over a TALI connection.If no response is received within the predetermined time period, theconnection may be reset and/or reestablished.

Table 1 below illustrates the packet structure of a test message. InTable 1, the test message includes a SYNC field, an OPCODE field, and aLENGTH field. The SYNC field is set to TALI, the OPCODE field is set totest, and the LENGTH field is set to 0. TABLE 1 Test Message OctetsField Name Description 0 . . . 3 SYNC ‘TALI’ 4 . . . 7 OPCODE ‘test’ 8 .. . 9 LENGTH Length = 0

FIG. 10 is a flowchart illustrating exemplary steps that may beperformed by a TALI process in monitoring the status of the connectionusing test messages. In step ST1, TALI process 322 sends a test messageto a peer on the other side of a connection. In step ST2, TALI process322 starts timers T1 and T2. The timer T1 may be used to determine whento send the next test message and the timer T2 may be used to determinethe time for receiving a valid response to the test message. In stepST3, timers T1 and T2 are compared to predetermined values. For example,the predetermined value for timer T1 may be set to a time period forsending the next test message. The timer value T2 may be set to apredetermined time period that is preferably less than the keep-alivetimer for TCP. For example, the timeout period may be set for two roundtrip times for the given connection. A method for measuring the roundtrip time of a connection will be discussed in more detail below.

In step ST4, TALI process 322 determines whether the timer T2 hasexpired or stopped. The timer T2 expires when it reaches the timeoutperiod set for T2. The timer T2 stops when an allow or a prohibitmessage is received. If the timer T2 has not expired or stopped, TALIprocess 322 continues to check the timer. In step ST5, if TALI process322 determines that the timer T2 has expired, TALI process 322determines whether a valid response to the test message has beenreceived. As discussed above, a valid response to the test message maybe an allow message or a prohibit message. If a valid response has beenreceived, TALI process 322 determines whether timer T1 has expired orstopped, and, if so, sends another test message to the other side (stepsST6 and ST1). In step ST7, if a valid response has not been received,TALI process 322 may reset and attempt to reestablish the connection.Since the timeout period is preferably less than that of a TCPconnection, monitoring of connection status using test messages providesmore efficient connection management that TCP. Moreover, because testmessages are periodically sent and acted upon, TALI connections can bereliably maintained.

Allow and Prohibit Messages

As discussed above, the TALI protocol provides allow and prohibitmessage for allowing and prohibiting communications over a TCPconnection without invoking TCP connection and establishment andtermination procedures. The allow message is sent in reply to a testquery or in response to an internal implementation event to indicatethat a TALI implementation is willing to carry SS7 service data over aTALI session. As used herein, a TALI session refers to TALI-levelconnection between endpoints. A TALI session may be created byestablishing a TCP connection followed by the exchange of allowmessages, as will be discussed in more detail below. The allow messageinforms the far end that SS7 traffic can be transmitted on theconnection. Allow is one of two possible valid replies to a testmessage. Before SS7 traffic can be carried over a connection, both endsof the connection are required to send allow messages to each other.Table 2 shown below illustrates an exemplary packet structure for anallow message. In Table 2, the allow message includes a SYNC field, anOPCODE field, and a LENGTH field. The SYNC field is set to TALI toindicate that the packet is a TALI packet. The OPCODE field is set to‘allo’ to identify an allow message. The LENGTH field is set to 0, sincethe service portion of the TALI packet does not carry any data. TABLE 2Allow Message Octets Field Name Description 0 . . . 3 SYNC ‘TALI’ 4 . .. 7 OPCODE ‘allo’ 8 . . . 9 LENGTH Length = 0

Like the allow message, the prohibit message is sent in reply to a testquery or in response to an internal implementation event. However,unlike the allow message, the purpose of the prohibit message is toindicate that a TALI implementation is not willing to carry SS7 serviceover the TALI session. The prohibit message informs the far end that SS7traffic cannot be transmitted over the connection. As long as one end ofthe connection remains prohibited, SS7 traffic cannot be carried overthe connection. Table 3 illustrates an exemplary packet structure for aprohibit message. In Table 3, the prohibit message includes a SYNCfield, an OPCODE field, and a LENGTH field. The SYNC field is set toTALI to identify the message as a TALI packet. The OPCODE field is setto ‘proh’ for prohibit. The LENGTH field is set to 0, since the messagedoes not carry any data in the service portion of the message. TABLE 3Prohibit Message Octets Field Name Description 0 . . . 3 SYNC ‘TALI’ 4 .. . 7 OPCODE ‘proh’ 8 . . . 9 LENGTH Length = 0

A prohibit acknowledgement message is a message sent by TALIimplementation in response to receiving a prohibit message from the farend of a connection. Receipt of a prohibit acknowledgement messageindicate that the prohibit message was received correctly and will beacted on accordingly. The side of a connection receiving a prohibitacknowledgement message can thus assume that no more data will betransferred over the connection and that it is okay to perform somedesired action associated with the connection. Table 4 shown belowillustrates a prohibit acknowledgement message according to anembodiment of the present invention. In Table 4, prohibitacknowledgement message includes a SYNC field, an OPCODE field, and aLENGTH field. The SYNC field may include the value TALI to indicate thatthe message is a TALI message. The OPCODE field may store the value‘proa’ to indicate that the message is a prohibit acknowledgementmessage. The LENGTH field may include a value of 0, because the serviceportion of the message does not contain any data. TABLE 4 ProhibitAcknowledgement Message Octets Field Name Description 0 . . . 3 SYNC‘TALI’ 4 . . . 7 OPCODE ‘proa’ 8 . . . 9 LENGTH Length = 0

FIG. 11 is a flowchart illustrating the advantages of using prohibit andacknowledgement messages to enable and disable connections. In step ST1,a TALI session is established between two nodes, node A and node B.Nodes A and B may each be any type of node previously described in whichit is desirable to implement a TALI protocol stack. For example, eithernode may be a signaling gateway, a media gateway controller, or anIP-capable SCP. Establishing a TALI session may include establishing aTCP connection between nodes A and B followed by the exchange of allowmessages between nodes A and B. Once the connection is established andcommunications are allowed, in step ST2, nodes A and B communicate usingthe TALI session. Such communication may include exchange of SS7 callsignaling messages, such as SCCP messages, TCAP messages, ISUP messages,and MTP3 messages. In step ST3, node A sends a prohibit message to nodeB. The reason for sending the prohibit message may be that node Adesires to perform a software upgrade. In step ST4, node A determineswhether a prohibit acknowledge message has been received. If a prohibitacknowledge message has not been received, node A may retransmit theprohibit message.

In step ST5, once node A receives the prohibit acknowledge message, nodeA can assume that data will not be received from node B over theprohibited connection. Accordingly, the manager of node B can performsome desired action, such as a software upgrade. When the desired actionis complete, in step ST6, node A can send an allow message to node Bover the connection. Once node B receives the allow message, node B canresume communications over the disabled connection. Because a transportadapter layer interface connection can be allowed and prohibited withoutinvoking TCP connection establishment and termination procedures, thetime and processing resources required for these operations are reducedover conventional TCP procedures.

Performance Measurement and Version Identification

According to another aspect of the invention, messages may be sentbetween TALI implementation to measure performance of a specificconnection and to communicate the TALI version number betweencommunication endpoints. One performance measurement that may be ofinterest is the round trip time. The round trip time is the time for amessage to travel from one side of a connection to the other and back.The vehicle for measuring the round trip time according to the presentembodiment includes a monitor message and a monitor acknowledgementmessage. A monitor message provides a generic echo capability that canbe used by a TALI implementation in order to measure the round triptime. Table 5 shown below is an example packet structure for the monitormessage. In Table 5, the monitor message includes a SYNC field, anOPCODE field, a LENGTH field, a version label field, and a Data field.The SYNC field identifies the monitor message as a TALI message. TheOPCODE field includes the value ‘moni’ to identify the message as amonitor message. The LENGTH field includes the length of the dataportion of the monitor message, which contains vendor-dependent data.The version label field in the monitor message may be used tocommunicate the TALI version number to the far end of a connection. Thepossible version label field values xxx.yyy specify the major and minorTALI version numbers. For example, a version label field value of001.000 specifies TALI version 1.0. TABLE 5 Version Control ‘moni’Message Octets Field Name Description Type of Field 0 . . . 3 SYNC‘TALl’ 4 byte Ascii text 4 . . . 7 OPCODE ‘moni’ 4 byte Ascii text 8 . .. 9 LENGTH Length (include the Integer version label and data fields) 10. . . 21 VER. LABEL ‘vers xxx.yyy’ 12 byte Ascii text 22 . . . X DataVendor Dependent Variable Maximum length of this message (as coded inbytes 8-9, and stored in bytes 10-x) should not exceed 200 bytes

In response to receiving a monitor message, a TALI session preferablysends a monitor acknowledgement message. Table 6 shown below illustratesan example packet structure for a monitor acknowledgement message. Inthe illustrated example, the monitor acknowledgement message includes aSYNC field, an OPCODE field, a LENGTH field, and a Data field. The SYNCfield stores the value TALI to indicate the start of a TALI packet. TheOPCODE field stores the value ‘mona’ to identify the packet as a monitoracknowledgement message. The LENGTH field stores the length of the dataportion of the monitor acknowledgement message. The data portion of themonitor acknowledgement message preferably includes the same data thatwas sent in the monitor message. The matching of data allows the monitormessage to be paired with the monitor acknowledgement message. TABLE 6Monitor Acknowledgement Message Octets Field Name Description 0 . . . 3SYNC ‘TALl’ 4 . . . 7 OPCODE ‘mona’ 8 . . . 9 LENGTH Length 10 . . . XData Vendor Dependent

FIG. 12 is a flowchart illustrating the use of the monitor message andthe monitor acknowledgement message to measure the round trip time of aconnection and to communicate the TALI version number to the far end ofa connection. In step ST1, a TALI implementation reads a timer valueassociated with the local machine and includes the timer value in amonitor message. In step ST2, the TALI implementation places its TALIversion number in the monitor message. The version number is used by theother side of a TALI connection to keep track of the version number. Forexample, upon receiving a monitor message, an endpoint may determinewhether the monitor message has a valid version label value in theversion label field. This may include comparing bytes located where theversion label field should be in the monitor message to a predeterminedlist of version values. If the value matches one of the values in thelist, then the endpoint stores that value as the TALI version for theother side. If the match is not found, the endpoint may store a defaultversion for the other side, e.g., 1.0. Since both sides of a connectionpreferably send monitor messages to each other and the monitor messagescan include the sending sides TALI version number, each side of theconnection can determine the current version of the other side.

In step ST3, the TALI implementation sends the monitor message to theother side of a connection. As discussed above, the other side of theconnection may use the version label to update the TALI version of thesending side. The other side of the connection changes the OPCODE of themessage from monitor to monitor acknowledgment and sends the messageback to the sending TALI implementation. In step ST4, the TALIimplementation receives the monitor acknowledgement message from theother side of the connection and extracts a timer value from the monitoracknowledgement message. In step ST5, the TALI implementation reads thelocal timer value when the monitor acknowledgement message was received.In step ST6, the TALI implementation computes the round trip time forthe connection based on the difference between the local timer valuewhen the monitor message was received and timer value read from themonitor acknowledgement message. Computing the round trip time in thismanner allows optimization of other timers, such as retransmissiontimers.

Authentication of Critical Messages

As indicated above, many of the messages sent between TALIimplementations can allow and/or prohibit communications over aconnection. Since such messages could be disastrous in atelecommunications environment, it is preferable that security messagesbe implemented to ensure that only authorized users can send thesemessages. One method for providing this security is to authenticatecritical messages. Examples of critical messages described herein areprohibit messages and test messages. To ensure that these messages aretransmitted by authorized users, encryption and/or authenticationprocedures can be used. In one example, a public key encryptionalgorithm, such as Rivest, Shamir, Adleman (RSA), can be used to verifythat the message originated from an authorized user. In order toauthenticate a message using a public key encryption algorithm, thesending node sends its public key to the receiving node. The sendingnode then signs the message using its private key. The receiving nodethen authenticates the message using the sending node's public key. Ifthe message authenticates correctly, i.e., if a valid TALI message isreceived, then the receiving node knows that the message came from anauthorized user. In this manner, the security of TALI connections can beincreased.

According to another aspect of the invention, critical messages may beauthenticated in a different manner using a public key cryptosystem. Forexample, a sender and a receiver may exchange public keys. That is, thesender S may send S's public key to the receiver R, and R may send R'spublic key to S. S may then encrypt a critical message, such as aprohibit message using R's public key. When R receives the message, Rmay decrypt the message using R's private key. If the message decryptscorrectly, R knows that the message comes from someone who has access toR's public key. R may then encrypt a response message, such as aprohibit acknowledgement message, using S's public key. R may then sendthe message to S. S may decrypt the message using S's private key. Ifthe message decrypts correctly, S knows that the message originated fromsomeone with access to S's public key. In this manner, two-wayauthentication may be achieved.

It will be understood that various details of the invention may bechanged without departing from the scope of the invention. Furthermore,the foregoing description is for the purpose of illustration only, andnot for the purpose of limitation—the invention being defined by theclaims.

1. A method for processing transport adapter layer interface (TALI)messages received over a stream-oriented connection, the methodcomprising: (a) receiving a plurality of TALI messages over astream-oriented connection; (b) identifying the beginning of each of theTALI messages using a first field in each of the TALI messages; (c)identifying the end of each of the TALI messages using a second field ineach of the TALI messages; and (d) extracting individual TALI messagepackets using the first and second fields.
 2. The method of claim 1comprising identifying the content of each of the TALI messages using athird field in each of the TALI messages.
 3. The method of claim 1wherein receiving a plurality of TALI messages over a stream-orientedconnection includes receiving a plurality of TALI messages over atransmission control protocol (TCP) connection.
 4. The method of claim 1wherein identifying the beginning of each of the TALI messages includesidentifying each of the TALI messages using a SYNC field in each of theTALI messages.
 5. The method of claim 1 wherein identifying the end ofeach of the TALI messages using a second data field includes identifyingthe end of each of the TALI messages using a LENGTH field for specifyingthe length of a data portion of each of the TALI messages.
 6. The methodof claim 2 wherein identifying the content of each of the TALI messagesusing a third data field includes identifying the content of each of theTALI messages using an OPCODE field for specifying the content of eachof the TALI messages.
 7. The method of claim 1 wherein a data portion ofeach of the TALI messages carries SS7 information.
 8. A computer programcomprising computer-executable instructions embodied in acomputer-readable medium for performing steps comprising: (a) receivinga plurality of TALI messages over a stream-oriented connection; (b)identifying the beginning of each of the TALI messages using a firstfield in each of the TALI messages; (c) identifying the end of each ofthe TALI messages using a second field in each of the TALI messages; and(d) extracting individual TALI message packets using the first andsecond fields.
 9. The computer program product of claim 8 comprisingidentifying the content of each of the TALI messages using a third fieldin each of the TALI messages.
 10. The computer program product of claim8 wherein receiving a plurality of TALI messages over a stream-orientedconnection includes receiving a plurality of TALI messages over atransmission control protocol (TCP) connection.
 11. The computer programproduct of claim 8 wherein identifying the beginning of each of the TALImessages includes identifying each of the TALI messages using a SYNCfield in each of the SS7 messages.
 12. The computer program product ofclaim 8 wherein identifying the end of each of the TALI messages using asecond data field includes identifying the end of each of the TALImessages using a LENGTH field for specifying the length of a dataportion of each of the TALI messages.
 13. The computer program productof claim 8 wherein identifying the content of each of the TALI messagesusing a third data field includes identifying the content of each of theTALI messages using an OPCODE field for specifying the content of eachof the TALI messages.
 14. The computer program product of claim 8wherein a data portion of each of the TALI messages carries SS7information.